Problems in the measurement of insertion loss of RFI filters under power-frequency load

A number of interesting problems arise in the measurement of insertion loss in a 50-ohm system of RFI filters while the rated ac or dc current is applied. This measurement is desirable when series inductors with cores other than air are utilized in the filter. Current standards do not, to the writer´s knowledge, require that filters be tested for insertion loss in the condition in which they are applied in practice, in this respect. It is the purpose of this letter to detail some of the considerations in what is an RF measurement in the presence of low-frequency ac, or dc (designated power frequency in this letter).